Rotary pump having swash type impeller

ABSTRACT

A rotary pump constructed for non-clogging operation with a swash plate type impeller of angle-shaped cross-section, the angle shape presenting a ridge which extends perpendicular to the impeller axis, thereby attaining improved balanced and nonvibrating pumping operation, this pump being operable with or without means for simultaneously shredding or comminuting any material carried by the liquid being moved through the pump.

United States Patent n 1 Petersen 1 Mar. 27, 1973 [541 ROTARY PUMP HAVING SWASH TYPE IMPELLER [75] Inventor: Paul I. Petersen, Stamford, Conn.

[73] Assignee: Dorr-Oliver Incorporated, Stamford,

Conn.

[22] Filed: Feb. 22, 1971 [21] Appl. N0.: 117,529

[52] US. Cl. .....241/46.ll, 241/73, 241/255, 241/261, 415/70, 415/121 [51] Int. Cl ..B02c 23/00 [58] Field of Search ..241/46.02, 46.11, 46.17, 69, 241/73, 255, 261; 415/70, 121, 215; 416/179, 180

[56] References Cited UNITED STATES PATENTS 2,012,602 8/1935 Forrester ..24l/69 3,113,734 12/1963 Neidl ..241/255 X 3,120,353 2/1964 Neidl v v ..241/261 X 3,375,983 4/1968 Von Eiff et a1. .,24l/46.1l

Primary Examiner-Granville Y. Custer, Jr. Att0rneyBurtsell J. Kearns and Theodore M. Jablon [5 7] ABSTRACT A rotary pump constructed for non-clogging operation with a swash plate type impeller of angle-shaped crosssection, the angle shape presenting a ridge which eX- tends perpendicular to the impeller axis, thereby attaining improved balanced and non-vibrating pumping operation, this pump being operable with or without means for simultaneously shredding or comminuting any material carried by the liquid being moved through the pump.

16 Claims, 15 Drawing Figures Patented March 27, 1973 4 Sheets-Sheet 1 INVENTOR.

PAUL PETERSEN FIG. 6

ATTORNEY.

Patented March 27, 1973 4 Sheets-Sheet 2 FIG. 2b

FIG. 2

TNVENTOR. PAUL PETERSEN ATTORNEY.

Patented March 27, 1973 3,722,804

4 Sheets-Sheet 5 INVENTOR. PAUL PETERS'EN aizmvwh ATTORNEY.

4 Sheets-Sheet 4.

FIG. 79

INVENTOR.

PAUL PETERSEN BY 7W ATTORNEY.

Patented March 27, 1973 x J 1: I n. a H 1 "n n z n n n z "u m I n E 5 u a u" .u 9 i a :m 1 m mm mm 6 m u u J u T l|| 2 3 in "m m" m 1 F n n w i w I, mm mm m mm "W m7 ROTARY PUMP HAVING SWASH TYPE IMPELLER This invention relates to improvements in rotary pumps having a swash plate type impeller to insure non-clogging operation.

As exemplified the US Pats. to Neidl Nos. 2,956,503; 3,005,597; 3,060,862; 3,067,960, and 3,329,354, the impeller in the type of pumps herein under consideration comprises a swash plate fixed upon the inner end of an impeller shaft. Such a swash plate is inclined relative to the impeller axis. This swash plate is surrounded closely by a cylindrical pump housing, and when rotated at suitable speed provides pumping action by drawing liquid through an axially disposed inlet neck of the pump housing, and discharging through a lateral upwardly directed outlet neck from the cylindrical body portion of the pump housing.

Furthermore, in the Neidl patents, the pumping action of the swash plate impeller is combined with a shredding or cutting action whereby material carried by the liquid being pumped may be comminuted during its passage through thepump. Such shredding is accomplished by forming the elliptically shaped side edges of the swash plate with serrations cooperating with complementary grooves provided internally along the periphery of the pump housing, to provide the cutting action incident to the pumping operation.

It is a main problem of this invention to provide a pump which eliminates vibrations imposed transversely as well as longitudinally upon the pump unit by the unbalanced swash plate type impeller heretofore in use, and requiring extra heavy construction of extra length, to compensate as far as possible for these vibrations. This vibration phenomenon also imposed limitation upon the admissible rotating speed of the impeller shaft. 7

One object of this invention is to provide a swash plate type impeller constructed to eliminate or minimize the aforementioned vibrations transversely as well as axially of the impeller shaft, combinedwith also allows for relatively shortening the axial length of the pump housing and of the machine as a whole for the sake of greater compactness, as well as weight reduction.

In order to allow for the removal of the shredding type impeller from the housing in theaxial direction, there are provided detachable cutter bars formed with the required complementary cutting grooves, with bars extending parallel to the impeller axis, being spaced from one another along the inner periphery of the pump housing. Complementary recesses are formed in the lateral elliptical edge portions of the angle-shaped I impeller plate, matching the spacing of the cutter bars.

greater uniformity of the pumping cycle, and greater;

compactness of the machine as a whole. Such vibrations have imposed limitations upon the operating speed of these pumps, even though dynamic balancing of the impeller was resorted to.

Furthermore, in a prior Neidl pump of the shredding type, the pump housing was split into a pair of half shells to be separated or unbolted. from each other. This construction would allow the serrations or teeth on the impeller plate to become disengaged from the grooves of the housing when removing the impeller. Therefore another object is to provide a pump .constructed and arranged so as to allow the shredding impeller to be withdrawn axially, without requiring the pump housing to be split.

Still another object is to provide screening means in the discharge area of the pump housing, which are readily accessible and exchangeable without requiring the dismantling of the pump.

The foregoing objects of the invention are attainable by the provision of a swash type impeller having a swash plate of angle shaped cross-sectional configuration presenting a ridge which extends perpendicular to the impeller axis, thereby attaining improved balanced and substantially nonvibrating pumping operation. This angular or folded shape ofthe improved swash plate When the impeller is rotated to a position where said complementary recesses are lined up or matched with the cutter bars, the impeller and shaft may be arcuate screening members removably attached thereto.

Other features and advantages will hereinafter appear.

As this invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, the present embodiment is illustrative and not -restrictive. The scope of the invention is defined by the appended claims rather than by the description preceding them, and all embodiments which fall within the meaning and range of equivalency of the claims are therefore intended to be embraced by those claims.

FIG. 1 is a longitudinal vertical part-sectional view of the rotary pump showing a swash plate type impeller of angle shaped cross section having a ridge line extending perpendicular to the impeller axis.

' FIG..2b is a reduced detail view of a hand hole cover,

taken on line 2b-.-2bin FIG. 2.

'FIG. 2a is an enlarged detail sectional view of a hold down or retainer device mounted on the hand hole cover, taken on line 2a-2a in FIG. 2b.

FIG. 3 is a further enlarged vertical sectional view taken on line 3-3 in FIG. 2, providing a more detailed showing of the angle-shaped impeller structure cooperating with the pump housing for pumping as well as shredding or comminution.

FIG. 3a is a detail sectional view taken on line 3a I 30 in FIG. 3, showing a complementary retainer device fixed to the pump housing.

FIG. 4 is a detail lateral end view of the impeller generally illustrating the angle shape of the impeller having serrated'edges for shredding.

FIG. 5 is a top view taken on line 55 in FIG. 4 of the impeller.

FIG. 6 is a side view taken on line 6-6 in FIG. 5 of the impeller.

FIG. 7 is a detail cross-sectional view of a stationary cylindrical shredder assembly taken from the pump housing and showing removable arcuate screen members as well as removable cutter bars.

FIG. 7a is a detail top view of one of the arcuate screen members, taken on line 7a-7a in FIG. 7.

FIG. 8 is a side view of the cylindrical cutter assembly taken on line 8-8 in FIG. 7.

FIG. 9 is a top view taken on line 9--9 in FIG. 8.

FIG. 10 is a detail front view of one of the cutter bars, taken on line lin FIG. 7.

FIG. 11 is a side view taken on line 11-11 in FIG.

The rotary pump unit according to this invention employs a novel swash plate type impeller 10 mounted upon and fixed to the inner end 11 of an impeller shaft 12.

The impeller comprises a hub portion 13 keyed at 13a to the inner end of the impeller shaft, and formed with a pair of convergingly inclined symmetrical end faces 14 and 15 of hub portion 13 defining between them the angle A-l (see FIG. 1). These converging end faces fit closely into a correspondingly shaped swash plate 16 having angular cross-sectional configuration.

Accordingly, this angular swash plate or impeller plate comprises a pair of symmetrical wing portions 17 and 18 between them constituting a ridge 1) which in turn extends perpendicular to the impeller axis, facing the axially disposed inlet neck 20 of the pump. The

planes of the outer faces of wing portions 17 and 18 intersect in a ridge line L which is perpendicular to the impeller axis. The hub portion 13 and the angular swash plate 16 are secured to each other as by means of weld connections 21 and 22 (see FIG. 4), while the impeller itself is secured to the impeller shaft by means of an axially disposed bolt 23 the head of which is countersunk into the ridge, with a plug screw 23a closing the recess formed by the countersink.

The impeller shaft rotates in a pair of horizontally spaced bearings, namely a forward bearing 24 and a rearward bearing 25, both mounted in a bearing section 26 of the pump unit which further comprises a housing section 27 surrounding, and cooperating with the impeller.

It will be seen that the rearward bearing is mounted in such a manner as to secure the impeller shaft against axial displacement relative to the pump housing, since the outer stationary race member 28 of the bearing is confined between a shoulder 29 and a removable end cover member 30, while the inner rotating race member 31 is confined between a shoulder 32 and a lock nut 33. The forward bearing 24, however, has an outer race member 34 that is axially unconfined.

Note that the forward end of the impeller shaft has an annular shoulder 35 (see FIG. 3) engaged by a complementary shoulder 36 of a sleeve member 37 surrounding the shaft and secured by tightening of screw bolt 23 of the impeller. The rearward end of sleeve 37 terminates adjacent the inner race member 38 of bearing 24, thereby securing the race member relative to an annular shoulder 39 of the impeller shaft. The outer race member 34 .is axially unconfined because of the clearances C-1 and C-2 respectively on either side.

A series of annular sealing members 40 surrounding the sleeve 37 and held in place by a retainer ring 41, provides a seal between the bearing section and the interior of the housing section or pump chamber surrounding the impeller.

The aforementioned housing section 27 of the pump unit comprises a cylindrical body portion 42, having an upwardly directed pump outlet neck 43, a forward closure member 44 having the aforementioned axially directed pump inlet neck 20, and an opposite rearward closure member 46 fixed to bearing section 26. The end closure members 44 and 46 are bolted to respective end flanges 47 and 48 of the cylindrical body por tion 42. Outlet neck 43 of the pump housing has inclined outwardly converging walls 49 and 50 provided each with a hand hole 53 and detachable cover plate 54, and parallel walls 51 and 52. These hand holes provide access to arcuate screen members 65, as will be furthermore described.

In a preferred form of the pump unit herein illustrated, the impeller as shaped and constructed according to this invention maybe employed in a combined pumping and shredding operation. For that purpose, the impeller has edge portions formed with serations or indentations cooperating with complementary grooves provided upon the interior of the cylindrical body portion of the housing. To that end, referring to FIGS. 4, 5, and 6, each of the inclined wings l7 and 18 of the impeller has a pair of elliptical side edge portions formed with serrations or indentions 55 directed parallel to a plane which extends perpendicular to the impeller axis. These indentations are thus shaped and arranged to cooperate with the teeth of cutter bars 58a, 58b, 58c, and 58d (see FIG. 2) to produce a shredding action, furthermore to be described. Each of the Wings 17 and 18 is furthermore defined by a straight terminal edge portion 56 intermediate the two side edge portions, and

parallel to the ridge 19. Each of the wings 17 and 18 cutter bars spaced apart,'namely an upper cutter bar 58a, a lower one 58b, and two pairs of lateral ones 58c and 58d respectively. These cutter bars are detachably mounted by screws 61 (see FIG. 3) upon the inner face of a cylindrical insert member 59 to constitute therewith a cutter bar assembly as clearly illustrated in FIGS. 7, 10 and 11. This cylindrical sub-assembly is insertable into the cylindrical body portion 42 of the housing section, and positioned and secured therein between the end closure members in the manner shown in FIGS. 2 and 3.

The cutter bars are seated in grooves or channels 60 formed internally of the cylindrical insert member, so as to extend parallel to one another and parallel to the axis of the insert member, and are secured in place as indicated by screws 61 (see FIG. 3).

The cylindrical insert member is furthermore formed with a pair of symmetrically arranged openings 62 and 63 of rectangular configuration, occupying the arcuate outlet flow area at the wide end of the outlet neck 43, the arcuate extent of that area being indicated by the angle A-2 (see FIG. 2). These openings 62 and 63 are spaced from each other by a relatively narrow web portion 64 (see FIG. 7) of the insert member, but wide enough to accommodate the upper cutter bar 58a.

From FIG. 2 it will now be noted that the two hand holes 53 provide convenient access to the respective screen members, allowing them to be removed for inspection. The inner mutually adjacent ends of the screen members are held in place by the specially shaped head portions 66 of a pair of horizontally disposed internal retainer screws (see FIGS. 3 and 3a) threaded into the respective end flanges 47 and 48 of he body portion 42. The outer ends of the screen members are held in place by a pair of set screws 67 and 68 (see FIGS. 2, 2a and 2b) carried by the respective cover plates 54. Thus after removal of such a cover plate, the adjacent screen member 65 may be lifted from its seat in the manner shown in FIG. 3a, the manipulation being further indicated (in dot-and-dash) in FIG. 2.

The impeller may be disconnected from the shaft, and removed from the pump housing in the following manner:

After disconnecting the outer closure member 44, the impeller is rotated to the position shown in FIG. 2, so that the ridge portion 19 of the impeller is positioned horizontally. The teeth of the two pairs of cutter bars 58c and 58d respectively with then lodge in, or register with recesses R-l, R-2, R-3, and R-4 respectively, which recesses are provided in the respective wing portions of the impeller (see FIGS. 2 and 4). Accordingly. (see FIG. 2), the left-hand upper cutter bar 58c then lodges in recess R-l, the lower left-hand cutter bar 580 lodges in recess 11-2, the upper right-hand cutter bar 58d lodges in recess R-3, and the lower right-hand cutter bar 58d lodges in recess R-4.

With the impeller held in this position relative to the cutter bars, and after loosening the bolt 23, the impeller can be pulled off the impeller shaft, and clear of the cutter bars.

I claim: 1. A rotary pump which comprises a pump housing having a cylindrical body portion provided with an outlet neck, a forward end closure member provided with an inlet neck, and an opposite rearward end closure member,

an impeller shaft mounted for rotation coaxial with said cylindrical body portion, and extending through said opposite end closure member, and having an inner end terminating within said body portion, 1

and a swash plate type impeller mounted on said inner end of the shaft, said impeller being of angleshaped cross-section,'the angle being symmetrical relative to the impeller axis, and presenting a ridge at the apex of the angle facing said inlet neck, and extending perpendicular to the impeller axis.

2. The rotary pump according to claim 1 wherein said impeller is provided with marginal serrations, and said body portion is provided internally with grooves complementary with said serrations for shredding or comminuting any material carried by the liquid being moved through the pump.

- 3. A rotary pump which comprise a pump housing having a cylindrical body portion provided with an outlet neck, a forward end closure member provided with an inlet neck, and an opposite rearward end closure member,

an impeller shaft mounted for rotation coaxial with said cylindrical body portion, and extending through said opposite closure member, and having an inner end terminating within said body portion, and an impeller mounted on said inner end of the impeller shaft, and shaped to provide a pair of symmetrical impeller faces inclined towards each other as well as inclined relative to the impeller axis, and in symmetrical relationship thereto, said inclined impeller faces defining an enclosed angle "with the apex thereof pointed towards said inlet neck, said apex in turn defining a ridge line intersecting with the axis of the impeller shaft perpendicular thereto, each said impeller face having a pairof symmetrical arcuate edge portion conforming to, and c-operating with the surrounding body portion of the housing to produce the pumping effect during rotation of the impeller, and having an intermediate straight edge portion parallel to said ridge line and sweeping over said opposite closure member during said rotation.

4. The rotary pump according to claim 3, wherein said outlet neck extends radially from said cylindrical body portion of the housing, and comprises a pair of inclined walls extending substantially tangential to the periphery of said cylindrical body portion, and converging towards each other, and a pair of parallel complementary walls interconnecting said inclined walls, each of said parallel walls being defined by correspondingly converging edges connected to respective adjoining inclined edges of the inclined walls, and by an arcuate bottom edge extending between the inner ends of respective converging edges and conforming to the curvature of said cylindrical body portion of the hous- 5. The rotary pump according to claim 4, wherein said cylindrical body portion of the housing has parallel end flanges for connection therewith of said end closure members, and wherein said parallel complementary walls of the outlet neck extend substantially in the respective planes of said end flanges.

6. The rotary pump according to claim 3, wherein said arcuate edge portions of the impeller are formed with serrations, and said cylindrical body portion is provided internally with complementary grooves coacting with said serrations to effect comminution of material carried by liquid moved through the pump, with the addition of arcuate screening means conforming to the curvature of said cylindrical body portion, and occupying the arcuate outflow passage area at the base of said outlet neck.

7. The pump according to claim 6, 'wherein said screening means are removably mounted in said outlet passage area, and wherein said outlet neck has at least one hand hole with removable cover plate therefor, adjacent said screening means.

8. The pump according to claim 3, wherein said outlet neck extends radially from said cylindrical body portion of the housing, and comprises a pair of inclined walls extending substantially tangential to the periphery of said cylindrical body portion, and con verging towards each other, and a pair of parallel complementary walls, each of said parallel walls being defined by correspondingly converging edges connected to respective adjoining inclined edges of the inclined walls, and by an arcuate bottom edge extend ing between the inner ends of respective converging edges and conforming to the curvature of said cylindrical body portion of the pump housing, wherein said arcuate edge portions of the impeller faces are formed with serrations, and the wall of said cylindrical body portion of the housing is provided with complementary grooves coacting with said serrations to effect comminution of material carried by liquid moved through the pump, wherein arcuate removable screening means are provided conforming to the curvature of said cylindrical body portion, and occupying the arcuate outflow passage area at the base of said outlet neck, and wherein said outlet neck has at least one hand hole with removable cover plate therefor, adjacent said screening means.

9. A rotary pump which comprises a pump housing having a cylindrical body portion provided with an outlet neck, a forward end closure member provided with an inlet neck, and an opposite rearward end closure member,

an impeller shaft mounted for rotation co-axial with said cylindrical body portion, said shaft extending through said opposite end closure member and having an inner end terminating within said body portion,

an impeller mounted on said inner end of the impeller shaft, and shaped to provide a pair of symmetrical impeller faces inclined towards each other as well as inclined relative to the axis of said shaft and in symmetrical relationship thereto, said inclined impeller faces defining an enclosed angle with the apex thereof pointed towards said inlet neck, said apex in turn defining a ridge line intersecting with the axis of the impeller shaft perpendicular thereto, each said impeller face having a pair of symmetrical arcuate edge portions provided with serrations, and having an intermediate straight edge portion parallel to said ridge line and sweeping over said opposite closure member during rotation of said impeller,

and a stationary cutter assembly providing complementary cutting grooves cooperating with said serrations, and comprising a cylindrical insert member concentrically fitted into said body portion of the housing, and provided with screening means occupying the arcuate through flow area at the base of said outlet neck, and a plurality of cutter bars parallel to the impeller axis detachably fixed to the inner face of said insert member, spaced from one another along the inner periphery thereof, and formed with cutting grooves complementary to, and cooperating with said serrations to comminute material carried by the liquid moved through the pump.

10. The pump according to claim 9, wherein said screening means are removably mounted on said insert member, and wherein said outlet neck has a hand hole with a removable cover plate, adjacent said screening means.

11. The pump according to claim 9, wherein said outlet neck extends radially from said cylindrical body portion of the housing, and comprises a pair of inclined walls extending substantially tangential to the periphery of said cylindrical body portion, and converging towards eac other, and a pair of parallel complementary walls interconnecting said inclined walls, each of said parallel walls being defined by correspondingly converging edges connected to respective adjoining inclined edges of the inclined walls, and by an arcuate bottom edge extending between the inner ends of respective converging edges and conforming to the curvature of said cylindrical body portion of the housing, wherein said screening means are removably mounted on said cylindrical insert member, and wherein at least one of said inclined walls has a hand hole with removable cover plate therefor, adjacent said screening means.

12. The pump according to claim 9 wherein said insert member has a pair of symmetrically arranged rectangular openings, and a pair of correspondingly shaped screen members removably mounted, one in each said rectangular opening, and wherein said outlet neck has a hand hole adjacent each respective screen member, provided with removable cover-plate therefor, adjacent said screening means.

13. The pump according to claim 9, wherein said outlet neck extends radially from said cylindrical body portion of the housing and comprises a pair of inclined walls extending substantially tangential to the periphery of said cylindrical body portion, and converging towards each other, and a pair of parallel complementary walls interconnecting said inclined walls, each of said parallel walls being defined by correspondingly converging edges connected to respective adjoining inclined edges of the inclined walls, and by an arcuate bottom edge extending between the inner ends of respective converging edges and conforming to the curvature of said cylindrical body portion of the housing, and wherein said insert member has a pair of symmetric-arranged rectangular openings, and a pair of correspondingly shaped screen members removably mounted one in each of said rectangular openings, each said screen member being accessible and removable through a respective adjacent hand hole in said outlet neck.

14. The pump according to claim 9, wherein the arcuate edge portions of the impeller are provided with recesses spaced from one another to match the spacing of the cutter bars, and extending parallel to the axis of the impeller shaft, said recesses furthermore having a cross-sectional shape corresponding to the cross-sectional profile of the cutter bars, thereby allowing the.

impeller to be axially withdrawn from the pump housing after the impeller has been rotated to a position where said recesses register with respective cutter bars.

15. In a rotary pump a swash plate type impeller of angle shaped cross-sectional configuration the angle being symmetrical relative to the impeller axis, and presenting a ridge at the apex of said angle, extending perpendicular to the impeller axis.

16. The impeller according to claim 15, wherein each of the external inclined pumping faces of the impeller has a groove, both said grooves extending in a common plane with the impeller axis, and an auxiliary cutter bar isdetachable mounted in each groove.

i t i i l 

1. A rotary pump which comprises a pump housing having a cylindrical body portion provided with an outlet neck, a forward end closure member provided with an inlet neck, and an opposite rearward end closure member, an impeller shaft mounted for rotation coaxial with said cylindrical body portion, and extending through said opposite end closure member, and having an inner end terminating within said body portion, and a swash plate type impeller mounted on said inner end of the shaft, said impeller being of angle-shaped cross-section, the angle being symmetrical relative to the impeller axis, and presenting a ridge at the apex of the angle facing said inlet neck, and extending perpendicular to the impeller axis.
 2. The rotary pump according to claim 1 wherein said impeller is provided with marginal serrations, and said body portion is provided internally with grooves complementary with said serrations for shredding or comminuting any material carried by the liquid being moved through the pump.
 3. A rotary pump which comprises a pump housing having a cylindrical body portion provided with an outlet neck, a forward end closure member provided with an inlet neck, and an opposite rearward end closure member, an impeller shaft mounted for rotation coaxial with said cylindrical body portion, and extending through said opposite closure member, and having an inner end terminating within said body portion, and an impeller mounted on said inner end of the impeller shaft, and shaped to provide a pair of symmetrical impeller faces inclined towards each other as well as inclined relative to the impeller axis, and in symmetrical relationship thereto, said inclined impeller faces defining an enclosed angle with the apex thereof pointed towards said inlet neck, said apex in turn defining a ridge line intersecting with the axis of the impeller shaft perpendicular thereto, each said impeller face having a pair of symmetrical arcuate edge portion conforming to, and c-operating with the surrounding body portion of the housing to produce the pumping effect during rotation of the impeller, and having an intermediate straight edge portion parallel to said ridge line and sweeping over said opposite closure member during said rotation.
 4. The rotary pump according to claim 3, wherein said outlet neck extends radially from said cylindrical body portion of the housing, and comprises a pair of inclined walls extending substantially tangential to the periphery of said cylindrical body portion, and converging towards each other, and a pair of parallel complementary walls interconnecting said inclined walls, each of said parallel walls being defined by correspondingly converging edges connected to respective adjoining inclined edges of the inclined walls, and by an arcuate bottom edge extending between the inner ends of respective converging edges and conforming to the curvature of said cylindrical body portion of the housing.
 5. The rotary pump according to claim 4, wherein said cylindrical body portion of the housing has parallel end flanges for connection therewith of said end closure members, and wherein said parallel complementary walls of the outlet neck extend substantially in the respective planes of said end flanges.
 6. The rotary pump according to claim 3, wherein said arcuate edge portions of the impeller are formed with serrations, and said cylindrical body portion is provided internally with complementary grooves coacting with said serrations to effect comminution of material carried by liquid moved through the pump, with the addition of arcuate screening means conforming to the curvature of said cylindrical body portion, and occupying the arcuate outflow passage area at the base of said outlet neck.
 7. The pump according to claim 6, wherein said screening means are removably mounted in said outlet passage area, aNd wherein said outlet neck has at least one hand hole with removable cover plate therefor, adjacent said screening means.
 8. The pump according to claim 3, wherein said outlet neck extends radially from said cylindrical body portion of the housing, and comprises a pair of inclined walls extending substantially tangential to the periphery of said cylindrical body portion, and converging towards each other, and a pair of parallel complementary walls, each of said parallel walls being defined by correspondingly converging edges connected to respective adjoining inclined edges of the inclined walls, and by an arcuate bottom edge extending between the inner ends of respective converging edges and conforming to the curvature of said cylindrical body portion of the pump housing, wherein said arcuate edge portions of the impeller faces are formed with serrations, and the wall of said cylindrical body portion of the housing is provided with complementary grooves coacting with said serrations to effect comminution of material carried by liquid moved through the pump, wherein arcuate removable screening means are provided conforming to the curvature of said cylindrical body portion, and occupying the arcuate outflow passage area at the base of said outlet neck, and wherein said outlet neck has at least one hand hole with removable cover plate therefor, adjacent said screening means.
 9. A rotary pump which comprises a pump housing having a cylindrical body portion provided with an outlet neck, a forward end closure member provided with an inlet neck, and an opposite rearward end closure member, an impeller shaft mounted for rotation co-axial with said cylindrical body portion, said shaft extending through said opposite end closure member and having an inner end terminating within said body portion, an impeller mounted on said inner end of the impeller shaft, and shaped to provide a pair of symmetrical impeller faces inclined towards each other as well as inclined relative to the axis of said shaft and in symmetrical relationship thereto, said inclined impeller faces defining an enclosed angle with the apex thereof pointed towards said inlet neck, said apex in turn defining a ridge line intersecting with the axis of the impeller shaft perpendicular thereto, each said impeller face having a pair of symmetrical arcuate edge portions provided with serrations, and having an intermediate straight edge portion parallel to said ridge line and sweeping over said opposite closure member during rotation of said impeller, and a stationary cutter assembly providing complementary cutting grooves cooperating with said serrations, and comprising a cylindrical insert member concentrically fitted into said body portion of the housing, and provided with screening means occupying the arcuate through flow area at the base of said outlet neck, and a plurality of cutter bars parallel to the impeller axis detachably fixed to the inner face of said insert member, spaced from one another along the inner periphery thereof, and formed with cutting grooves complementary to, and cooperating with said serrations to comminute material carried by the liquid moved through the pump.
 10. The pump according to claim 9, wherein said screening means are removably mounted on said insert member, and wherein said outlet neck has a hand hole with a removable cover plate, adjacent said screening means.
 11. The pump according to claim 9, wherein said outlet neck extends radially from said cylindrical body portion of the housing, and comprises a pair of inclined walls extending substantially tangential to the periphery of said cylindrical body portion, and converging towards each other, and a pair of parallel complementary walls interconnecting said inclined walls, each of said parallel walls being defined by correspondingly converging edges connected to respective adjoining inclined edges of the inclined walls, and by an arcuate bottom edge extending between the inner ends of respective converging edges aNd conforming to the curvature of said cylindrical body portion of the housing, wherein said screening means are removably mounted on said cylindrical insert member, and wherein at least one of said inclined walls has a hand hole with removable cover plate therefor, adjacent said screening means.
 12. The pump according to claim 9 wherein said insert member has a pair of symmetrically arranged rectangular openings, and a pair of correspondingly shaped screen members removably mounted, one in each said rectangular opening, and wherein said outlet neck has a hand hole adjacent each respective screen member, provided with removable cover-plate therefor, adjacent said screening means.
 13. The pump according to claim 9, wherein said outlet neck extends radially from said cylindrical body portion of the housing and comprises a pair of inclined walls extending substantially tangential to the periphery of said cylindrical body portion, and converging towards each other, and a pair of parallel complementary walls interconnecting said inclined walls, each of said parallel walls being defined by correspondingly converging edges connected to respective adjoining inclined edges of the inclined walls, and by an arcuate bottom edge extending between the inner ends of respective converging edges and conforming to the curvature of said cylindrical body portion of the housing, and wherein said insert member has a pair of symmetric-arranged rectangular openings, and a pair of correspondingly shaped screen members removably mounted one in each of said rectangular openings, each said screen member being accessible and removable through a respective adjacent hand hole in said outlet neck.
 14. The pump according to claim 9, wherein the arcuate edge portions of the impeller are provided with recesses spaced from one another to match the spacing of the cutter bars, and extending parallel to the axis of the impeller shaft, said recesses furthermore having a cross-sectional shape corresponding to the cross-sectional profile of the cutter bars, thereby allowing the impeller to be axially withdrawn from the pump housing after the impeller has been rotated to a position where said recesses register with respective cutter bars.
 15. In a rotary pump a swash plate type impeller of angle shaped cross-sectional configuration the angle being symmetrical relative to the impeller axis, and presenting a ridge at the apex of said angle, extending perpendicular to the impeller axis.
 16. The impeller according to claim 15, wherein each of the external inclined pumping faces of the impeller has a groove, both said grooves extending in a common plane with the impeller axis, and an auxiliary cutter bar is detachable mounted in each groove. 